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Moving Sound Around: Digital Sound Files and the ContentDepot provides an overview of the process and choices involved in preparing digital sound files for distribution via the PRSS. Once you have prepared your files, you can use the PRSS ContentDepot to deliver sound files to stations for audition or broadcast use.
Much of the information contained in this module came from a presentation given by independent producer Stephen Hill (Hearts of Space) at the 2003 AIR Producers Intensive in San Francisco. Out of that presentation, NPR Distribution developed this training module for use by program producers, distributors, and station personnel who want to learn how new technologies can help streamline the process of distributing radio programs.
If you have no background in this area, we encourage you to start at the beginning of the module and work your way through. If you already have some understanding and/or experience in working with sound files, you may choose individual topics that will help to round out your knowledge.
Information contained in this training module does not constitute an endorsement of any of the organizations or products listed herein, and all content is subject to change.
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Introduction
In this training module, you will learn the basics of preparing digital sound files for PRSS distribution. The navigation is arranged to help you focus on the main questions addressed in each section of the module:
- Benefits: What are the benefits of using sound files to deliver audio?
- Making Choices: What platforms or tools can you use to create and encode sound files? What sound file formats will you need?
- The Process: What is the process for creating, encoding, and delivering sound files? What Internet issues should you be aware of when delivering sound files?
- Metadata: What is metadata and how can you use it to improve the distribution of information about your program(s)?
- Getting Started: What additional resources are available to help you get started creating, encoding, and delivering sound files?
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Benefits of Digital File Transmission
Why do most producers choose electronic file submission over submitting programs on physical media (DAT, CD, and tape)? Electronic file submission offers significant benefits to certain producers, including:
- faster delivery (faster than real-time, with a high-speed Internet connection);
- more efficient delivery of audio files;
- reduced postage and shipping costs;
- extended deadlines;
- no charge for "assisted ingest" (creation of audio files by PRSS staff)
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Before you can start creating and delivering files electronically, you need to make some choices. For example, you need to decide:
- what platform you will use;
- what file formats you will need to meet your distribution needs;
- what tools you will use to create and encode your files.
Please note that the available tools depend somewhat on the platform you use and the kinds of files that you need. |
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 You may use a PC or a MAC to create and encode your sound files. Which platform you use does not matter, as long as the files you submit meet PRSS file standards (see 'F').
Note: MAC has always been an integrated multimedia platform. PCs require a sound card, and versions of Windows older than Windows XP require additional software before they can be used to create sound files for delivery to the PRSS. |
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WAV files, AIFF, MP2, MP3, RealMedia...there are many possible formats for sound files. What format should you use for your production material and for your master sound file (the original, electronic file that you will keep on your system)? To get the highest possible audio quality for production and mastering purposes, use a non-data-reduced format, such as linear PCM (pulse code modulation), BWAV, WAV, AIFF, or SD2.
Note: Transcoding (converting your sound files from one format to another) degrades audio quality. Multiple transcodings (converting your master file from one format to another and then converting the newly encoded file to still another format) degrades audio quality further. Always begin with your non-data-reduced master sound file when encoding. Remember, additional transcodings may occur after you upload the file to the ContentDepot for delivery, as the program wends its way through the stations' broadcast facilities.
What format(s) do you need to use for your sound files?
That depends on the purpose for which each file will be used. The PRSS ContentDepot accepts broadcast-quality sound files for satellite transmission, as well as audition and promo files for your program. This table explains which file formats are appropriate for various purposes associated with PRSS distribution.
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File Purpose: |
Suitable Formats: |
Data Reduction: |
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master sound file
(the non-data-reduced file used as the source file when encoding) |
Linear PCM (pulse code modulation)
BWAV (Broadcast)
WAV (PC)
AIFF (Mac)
SD2 (Mac) |
None |
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broadcast-quality Sound File
(for ContentDepot delivery to stations) |
MP2 (MPEG 1, Layer II)
(Files must meet PRSS file standards. (*see 'F') ) |
Limited |
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audition files
(for stations to download manually) |
MP3 (MPEG 1, Layer III) |
Significant |
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Making Choices: Tools
 To record, edit, and mix digital sound files, you need a Digital Audio Workstation. The actual hardware and software of your workstation will depend on a number of factors, including:
- your platform (PC or Mac);
- the editing and encoding features you need; and
- how much you are willing to pay for software.
Many products are available for creating and working with sound files. These products generally include the following common features:
- non-destructive visual editing (allows experimenting because your master file is not overwritten until you save);
- files remain editable throughout the production process; and
- multiple file formats supported.
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The following table lists some common digital audio tools and indicates which industries/groups use them.
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Tool(s): |
Used By: |
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Pro Tools |
Music industry, film, TV, stations, independent producers |
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Cool Edit/
Adobe Audition |
Stations, independent producers |
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Sadie
Yamaha
Roland
Tascam
Mackie |
Music production facilities |
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Sound Forge |
Independent artists and producers |
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AudioVault
Enco
DALET
MediaTouch
Scott Systems
DaVID |
Stations, NPR Programming/Engineering, NOC |
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Links to more information about many of these tools are available in the Getting Started section of this module.
Once you have your digital audio workstation set up, you will need encoding software to convert your master sound file into file types that can be used by the ContentDepot. The first step is to check if your production software can already encode files in the appropriate formats. If not, you may want to check with the software manufacturer for any freeware or plug-ins that may be available.
Batch encoders will let you convert your original master sound file into multiple file formats. For example, you could make two copies of your master sound file at once—one in MP2 format, for distribution to stations, and another in MP3 format, for use as audition audio.
There are many encoding products available on the market. NPR Distribution does not endorse any of these products or guarantee their suitability for this purpose. We encourage you to carefully research any product in which you are interested in to make sure it is compatible with your platform;
- can convert from your master sound file format;
- can convert to all the required encoding formats; and
- can support future upgrades as new encoding standards are developed.
Please keep in mind that technology changes rapidly, and PRSS standards for electronic files are subject to change at any time.
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The Process
The process of preparing digital sound files for distribution via the PRSS involves three basic steps:
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Digital Sound Files and the ContentDepot1. Creating Audio Files
Based on your needs and the resources that are available to you, you will decide how to create your production audio and master sound file. To review considerations and appropriate formats for master sound files, see the information about production audio and master sound files, elsewhere in this module. To learn more about specific tools you can use to create your files, go to the Getting Started section of this module. |
2. Encoding Audio Files
Once you have created your master sound file, you need to encode the file into the proper format for ContentDepot use. For example, you will encode your broadcast audio as MP2, but audition audio as MP3. If you are using a batch encoder, you can make multiple conversions in one session when necessary, but always begin with your master sound file. This way, you get the highest possible audio quality and avoid the degradation associated with multiple conversions from one format to another.
You may use the tools of your choice to encode your files, but you must set the encoding parameters correctly for each PRSS file. The relevant encoding parameters are:
- Mode
- Bit rate
- Sampling rate
- Word length
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All broadcast audio and promos that you upload to the ContentDepot must be encoded according to the PRSS file specifications. Files that do not meet these specifications may not upload correctly or may cause problems for stations when they are delivered.
The Producer Guide includes the specifications for encoding parameters in broadcast-quality sound files (see 'F').
The PRSS does not presently require specific encoding parameters for audition audio submitted to the ContentDepot. |
3. Delivering Audio Files
Internet issues relating to file delivery: How efficiently your sound files are delivered to the NOC depends greatly on the equipment and bandwidth available at your facility. Are you sending files over a T-1 line (1.544 Mbps)? Via ISDN (128 Kbps)? If you're using DSL, the bit rate can vary, and most ADSL and cable modem systems definitely provide limited upload speed. If you're using a dial-up modem, remember that programs in the PRSS broadcast-quality format upload at 120 Mb/hour for stereo files. At this rate, a single program could tie up your line for hours—or time out your connection! Upgrading your connection will improve your transmission capability.
If you're uncertain about how much bandwidth you have available, use our bandwith test to learn more about your local resources.
If you have a slow connection and you are unable to upgrade, consider sending your files at off-peak times of day, when traffic is lighter. This can be particularly helpful if you are using shared services, such as cable modems, which upload files much more slowly during periods of heavy use. |
Delivering sound files to the ContentDepot: When you are ready to deliver your broadcast-quality sound files to the PRSS, login to the ContentDepot and navigate to the correct episode page to upload your files. (You must create the episode page before you can upload audio.) The ContentDepot Online Help system is available to help you throughout the process. Just click the Help link at the top of any page to go to the Index of Topics.
Each time you create an episode in the ContentDepot, you will also be asked to provide certain information (metadata) associated with that episode, including:
Episode Title
- Ingest Type (how the audio will come into ContentDepot)
- Delivery Type (how the audio will go out to stations)
- Begin Air Date and Time (the earliest date/time on which stations may broadcast this episode)
- End Air Date and Time (the latest date/time on which stations may broadcast this episode)
In addition, you may choose to include optional metadata about the episode, such as:
- Rundowns
- Promos
- Credits (e.g., for producers, underwriters, hosts)
- Promotional Text
Delivering files to the ContentDepot: The PRSS ContentDepot is a web-based service that provides a single location for programs, program information, and other related elements. The ContentDepot facilitates a powerful exchange of public radio program assets and information between program producers or distributors and stations. This means the most current program information is always available throughout the public radio community—in particular to station program directors. Producers or distributors who are registered with the PRSS and have an active account may use the ContentDepot to distribute their programs.
Audio and graphic files can be uploaded directly to the ContentDepot episode page. Please notify your Public Radio Services representative at 202.513.2600 when you are ready to begin distributing a program.
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Metadata is the information or data that accompanies a piece of digitized content. The term metadata can be applied to any data related to a piece of content, so when you submit an broadcast audio file to the ContentDepot, all accompanying information necessary to process and describe your program (e.g., episode title, episode description, rundown, file size, program length, etc.) is metadata. |
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Getting Started
The following links lead to additional information about various topics relating to digital audio production, encoding, and delivery. Information contained herein does not constitute an endorsement of any of the organizations or products listed, and all content is subject to change.
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The following links lead to additional information about various topics relating to digital audio production, encoding, and delivery. Information contained herein does not constitute an endorsement of any of the organizations or products listed, and all content is subject to change.
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